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Answer:
B. 9x² +15x -6
Step-by-step explanation:
The composition operator means that function f is applied to function g:
[tex](f\circ g)(x)=f(g(x))=f(3x-1)\\\\=(3x-1)^2+7(3x-1)\\\\=9x^2-6x+1+21x-7\\\\\boxed{(f\circ g)(x)=9x^2+15x-6}\qquad\textbf{matches B}[/tex]